Blast hole liner with integral weight pocket

ABSTRACT

A reinforced, flat-storable, waterproof blast hole liner with an integral pocket for receiving weighting material. The liner includes a flattened, flexible, waterproof inner tube having a waterproof seal at its lower end and a length-to-diameter ratio of at least 20/1. A flexible tubular outer sheath sheaths the inner liner and has a waterproof seam extending transversely of its lower end. The seam has a midpoint and laterally extending ends defining two seam halves, one seam half being folded upon and joined along its length to the other seam half to form an exteriorly accessible pocket into which weighting material may be placed. The sealed bottom end of the inner tube extends into close proximity with the seam at the bottom end of the sheath. The weighting material carried in the pocket anchors the inner tube at the bottom of a blast hole.

United States Patent [1 1 Mesia [451 May 6,1975

[75] Inventor: Charles R. Mesia, Mt. Iron, Minn.

[73] Assignee: Mesabi Jobbers, Inc., Virginia,

Minn.

[221 Filed: Nov. 9, 1973 [21] Appl. No.: 414,145

Primary ExaminerVerlin R. Pendegrass Attorney, Agent, or Firm-H. Dale Palmatier; James R. Haller [57} ABSTRACT A reinforced, flat-storable, waterproof blast hole liner with an integral pocket for receiving weighting material. The liner includes a flattened, flexible, waterproof inner tube having a waterproof seal at its lower end and a length-to-diameter ratio of at least 20/1. A flexible tubular outer sheath sheaths the inner liner and has a waterproof seam extending transversely of its lower end. The seam has a midpoint and laterally extending ends defining two seam halves, one seam half being folded upon and joined along its length to the other seam half to form an exteriorly accessible pocket into which weighting material may be placed. The sealed bottom end of the inner tube extends into close proximity with the seam at the bottom end of the sheath. The weighting material carried in the pocket anchors the inner tube at the bottom of a blast hole.

18 Claims, 7 Drawing Figures BLAST HOLE LINER WITH INTEGRAL WEIGHT POCKET BACKGROUND OF THE INVENTION In open pit mining, a series of vertical blast holes are formed in ore-bearing rock. Detonation of explosive charges which are inserted in the blast holes fragmentizes the rock, and enables the rock to be loaded into trucks or railroad cars for transportation to an ore refinery. Of the various explosive compositions which may be utilized, ammonium nitrate (preferably including fuel oil and popularly referred to as ANFO") has achieved great popularity and is widely used. The ammonium nitrate must be kept free of water which often collects in blast holes, since although wet ammonium nitrate will detonate, the detonation quality in fragmentizing rock is far from satisfactory. Although much of the water which ordinarily collects in blast holes is often pumped out before insertion of explosive charges, water of varying amounts ordinarily remains in the blast holes.

Various tubular plastic liners have been proposed for use with ANFO, the liners being weighted at their lower ends for introductional into blast holes and the ANFO then being poured into the inserted liners from the surface of the ground. To maintain their waterproof integrity, it is necessary that blast hole liners be resistent to cuts or abrasions caused by the often sharp inside surfaces of a blast hole when a liner is lowered into the blast hole. It is also desired that blast hole liners be fashioned to readily receive weighting material to enable easy insertion into a blast hole. The weighting material may be in the form of small, sharp rocks found at the blast hole site, and the liner must additionally resist punctures from such rocks. Blast hole liners should resist twisting during insertion into a blast hole, since undue twisting may foul the liner and interfere with the later insertion of explosive into the liner. Blast holes may extend to a depth of up to fifty feet or more and may have a diameter on the order of one foot.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a reinforced, waterproof, flat-storable blast hole liner with an integral weight pocket. The liner comprises a flattened, flexible, waterproof inner tube with a waterproof seal at its lower end to form a waterproof enclosure, the inner tube having a length-to-diameter ratio of at least l. The blast hole liner includes a flattened, flexible, tubular outer sheath which sheaths the inner tube and is substantially coextensive with the inner tube. The inner tube and sheath have open upper ends to receive an explosive charge. The sheath has a waterproof seam extending transversely of its lower end. The seam has ends extending laterally from its midpoint and which are folded about the midpoint and sealed together to form an exteriorly accessible pocket into which weighting material may be placed. The sealed end of the inner tube extends into close proximity with the bottom end of the sheath so that when weighting material is placed in the pocket and the blast hole liner is lowered into a blast hole, the inner liner is anchored at the bottom of the blast hole by the weighting material.

The sheath preferably projects outwardly slightly beyond the waterproof, folded and joined seam to form a graspable tab which may be used to manually open and close the pocket. For storage, the pocket is flattened with the folded and joined seam lying against the inner surface of the pocket, providing the pocket with a V-shaped configuration. The flattened inner liner, sheath, and V-shaped pocket permit the liner to be stored in roll form. When weighting material is placed in the pocket, the pocket acquires a generally coneshaped configuration with a downwardly oriented apex, this configuration permitting easy insertion of the blast hole liner into a blast hole.

In another embodiment, the invention relates to a method of making a blast hole liner wherein a flattened, flexible, inner tube having a waterproof seal at its lower end and sheathed within a flattened, flexible, tubular outer sheath, is provided, the sheath having a waterproof transverse seam at its lower end. The sealed lower end of the inner tube extends downwardly into close proximity with the transverse seam of the sheath, and may be coextensive with the sheath seam. The seam has a midpoint and generally laterally extending ends defining two seam halves. One seam half is folded back upon and joined to the other seam half along the length of the latter to form a pocket. The resulting joined seam is caused to lay fiat against the inner surface of the liner along the vertical midline of the liner, and the walls of the pocket are flattened to provide the pocket with a V-shaped configuration.

DESCRIPTION OF THE DRAWING FIG. 1 is a broken away elevational view of a blast hole liner of the invention shown prior to final assem- FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1 and is shown, for clarity, with exaggerated thicknesses;

FIG. 3 is a broken away elevational view of another blast hole liner of the invention shown prior to final assembly;

FIG. 4 is a cross-sectional view taken along lines 44 of FIG. 3 and is shown, for clarity, with exaggerated thicknesses;

FIG. 5 A, B and C are broken away perspective views of a blast hole liner of present invention in various stages of fabrication;

FIG. 6 is a broken away elevational view of a blast hole liner of the invention showing the pocket thereof containing weighting material; and

FIG. 7 is a broken away, cross-sectional view taken along lines 77 of FIG. 6 and is shown with greatly exaggerated thicknesses for clarity.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 5C, a blast hole liner of the invention designated generally as 10 comprises a waterproof, heat-sealable, plastic inner tube 12 having a length-to-diameter ratio of at least 20l, and a waterproof, heat-sealable, tubular plastic outer sheath l4 sheathing the inner tube and terminating in a flattened, V-shaped pocket 16. The pocket has an outwardly extending tab 18 which may be manually grasped and pulled outwardly to open the pocket into the position shown in FIG. 6 so that weighting material may be inserted.

In preparing a blast hole liner of the invention (with reference to FIG. 1), a heat-scalable, plastic inner tube 12 having a Iength-to-diameter ratio of not less than 2011 is provided adjacent its bottom end 12.] with a transverse waterproof heat seal 12.2. A sheath 14 having a laterally extending, heat-sealed, waterproof seam 14.1 adjacent its lower end 14.2 sheaths the inner tube. The upper ends of the inner tube and sheath are open to permit an explosive charge to be poured into the inner tube. The inner tube may extend above the upper end of the sheath, but desirably the inner tube and the sheath are substantially coextensive in length. As will be noted from FIGS. 1 and 2, the sealed end of the inner tube extends into close proximity with the lower end of the sheath, and the tube and sheath ends may be coextensive, and although separate heat seals for the tube and sheath are preferred to provide separate waterproof enclosures, a single heat seal may be used to seal both the inner tube and the sheath.

With reference to FIG. 5A, the seam 14.1 has ends 14.3 extending laterally from its midpoint 14.2 and which are folded together about the seam midpoint and which are heat-sealed together, as shown in FIG. 58, to form a pocket 20. As the pocket is formed, the inner tube 12 which extends into close proximity with the seam 14.2 takes on the contour of the pocket. The folded and joined seam 14.2 is laid back against the inner surface of the pocket, and the pocket is flattened, as shown in FIG. 5C, the midpoint 14.2 of the seam forming the apex of the V-shaped pocket. In the flattened condition shown in FIG. 5C, the entire blast hole liner may be wound up upon a spool, the end of the liner having the pocket being on the outside of the spool. The bottom edge 14.4 of the sheath 14 extends outwardly slightly from the seam 14.1 to form a manually graspable tab 18. From FIG. 5C, it will be appreciated that if the tab 18 is pulled outwardly, the pocket opens. The lower end of the inner tube 12 conforms closely to the configuration of the pocket, as is also depicted in FIG. 5C.

In use, the blast hole liner of the invention is transported to the blast site on an appropriate reel or spool. The diameter of the blast hole liner is ordinarily chosen so as to be substantially the same or slightly larger than the largest diameter to be encountered in the blast hole. The pocket of the blast hole liner is opened, for example, by pulling outwardly gently upon the tab 18. Weighting material, such as rocks or cuttings" 22 found at the blast hole site, is placed in the pocket, causing the pocket to bulge outwardly as shown in FIG. 6 to assume a downwardly pointing, generally conical or bullet-shaped configuration for easy insertion into the blast hole. The blast hole liner is lowered to the bottom of the blast hole, the weighting material 22 serving to pull the end of the liner downwardly. The outwardly extending tab 18 is believed to function to some extent as a rudder," or keel," in that it may bear against the inner surface of the blast hole as the liner is lowered, steadying the liner and reducing the tendency of the liner to twist.

FIG. 7 shows a partial cross-sectional view of the liner as the same is lowered into a blast hole. It is to be particularly noted that the weighting material 22, bearing downwardly upon the pocket, tends to pinch the inner tube 12 in the outer sheath 14 to prevent the tube and sheath from moving with respect to one another at their lower ends. When the blast hole liner has reached the floor of the blast hole, the bottom surface of the pocket flattens somewhat. The weighting material 22 in the pocket serves to anchor both the inner tube 12 and the outer sheath 14 from being pulled loose from the bottom of the hole when an explosive charge is inserted in the liner. It will be noted that both the inner liner and the outer sheath form separate waterproof enclosures each capable of fully protecting the explosive charge from contact with water in the blast hole.

It will be noted from FIG. 7 that the weighting material 22 is supported by no less than four plys of material (2 plys of the inner tube 12 and 2 plys of the outer sheath 14). Moreover, the explosive, when inserted in the blast hole liner at 23 in the FIG. 7, is protected from both the weighting material and the rough sides of the blast hole by at least two plys of material (one ply from the inner tube and one from the sheath).

FIGS. 3 and 4 depict a blast hole liner of the invention which includes an additional protective shell 24. The purpose of the shell is to offer greater resistence to tearing of the bottom of the blast hole liner as the same is lowered into a blast hole having a jagged interior surface. The outer shell 24 may extend the entire length of the blast hole liner, although it is desired that the length-to-diameter ratio of the shell 24 not exceed about 3/1 for purposes of economy and simplicity of manufacture. The shell extends substantially to the lower end 14.4 of the sheath. The outer shell 24 desirably is heat-sealed at 14.1 to the sheath 14, as shown best in FIG. 4. The pocket-forming operation described above and shown in FIGS. 5B and C is performed, the shell being included in the joint joining the seam halves 14.3 together. During this procedure, the shell 24 conforms to and becomes a part of the pocket of the liner. The resulting pocket retains the outwardly extending tab 18, as shown in FIG. 5C, and provides three protective plys of material at the bottom end of the liner between the explosive charge and both the weighting material and the rough sides of the blast hole.

Polyethylene is desired as the material for the inner tube 12. Low density polyethylene is preferred, and the walls of the inner tube may be about 0003-0012 inches in thickness, with a preferred thickness being on the order of 0.007 inches. Polyethylene is heat-scalable and provides excellent resistence to water from the blast hole and to oil from an explosive such as ANFO. The sheath 14 is preferably made of heat-scalable plastic material which is somewhat tougher and more resistent to tearing or puncturing than is polyethylene. Polybutylene of the type marketed under the tradename PB-l3/ by the Witco Chemical Corporation has demonstrated excellent physical resistence to tearing and puncturing, and is preferred as the material for the sheath 14. It has been found that the use of a polybutylene sheath having a thickness on the order of half that of the polyethylene inner tube yields satisfactory results from the standpoint of maintaining the waterproof integrity of the liner. In a preferred embodiment, polybutlylene film produced by blown film extrusion and having a thickness of about 0.004 inches is employed as the sheath material. Polyethylene tubing produced by blown film extrusion and having a thickness of about 0.007 inches is employed as the inner, explosivereceiving tube material. Polybutylene PB- 1 3 l as above identified, is a high molecular weight, isotactic polymer, synthesized from butene-l. Polybutylene requires a higher temperature for heat sealing than does polyethylene, and when polybutylene and polyethylene are used together as the sheath and inner tube materials, respectively, it is desired that the heat-sealed seam 14.1 of the sheath be formed separately from the heat seal 12.1 of the inner tube. FIGS. 1-4 show the seal 12.2 spaced slightly from the sealed seem 14.1. Other thermoplastic, flexible plastic films, such as the polyolifins and particularly including polypropylene, may be employed as the tube or sheath material. In the embodiment employing a short auxiliary shell 24 about the lower end of the blast hole liner, it is desired that the shell itself be made of polybutylene film. A single heat seal may be employed to seal the bottom of the shell 24 and the bottom of the sheath 14, as shown in FIGS. 3 and 4, although separate heat seals may be employed for the sheath and the shell if desired.

In manufacturing a blast hole liner of the invention, plastic tubing to be used in fashioning the inner tube 12 and the sheath is drawn from continuous, rolled lengths of flattened tubing. A section of sheath tubing is cut to length and is collapsed in accordion fashion around a relatively short assembly shaft mounted in cantilever fashion at one end to a support. The end of a continu ous length of inner tube tubing is provided with a heat seal 12.2 across its width, and the outer sheath is then drawn outwardly from the shaft around the inner tube. The inner tube is cut to the desired length, and the end of the sheath adjacent the sealed end of the inner tube is provided with a heat-sealed seam 14.1. The pocketforming procedure described above with reference to FIGS. 5B and C is then performed, and air is expelled from the sheath and inner tube through their open ends. If desired, the outer shell 24 which may be only a foot or so in length, may be assembled about the sheath and heat sealed to the sheath by the same heatsealing operation which forms the seam 14.1. The seam 14.1 is preferably straight and at right angles to the length of the liner, as shown in FIGS. 2 and 3. The seam may, however, angle upwardly or downwardly from its midpoint to yield a pocket which is respectively longer and narrower, or shorter and wider, than the pocket corresponding to the straight, right-angled seam referred to above.

The blast hole liners of the invention have been described above primarily with reference to waterproof, heat-scalable, thermosplastic materials. It will be understood that other flexible, waterproof materials may also yield acceptable results, such materials being provided with adhesive seals or other waterproof seals. Heat seals and heat-scalable materials are preferred, however, and the design of the blast hole liners of the invention lends itself readily to the use of common equipment adapted for heat sealing the edges of heatsealable plastic film.

Manifestly there has been provided a reinforced blast hole liner which is simple to fabricate, which has an integral, reinforced pocket adapted to receive weighting material, and which may conveniently be stored in its entirety in a flattened, roll form. Although a preferred embodiment of the present invention has been described, it should be understood that various changes, adaptations, and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

l. A reinforced, waterproof, flat-storable blast hole liner with integral weight pocket comprising:

a flattened, flexible, waterproof, tubular inner tube terminating at its lower end in a waterproof seal and having a length-to-diameter ratio of at least 20/1;

a flattened, flexible, waterproof, tubular outer sheath substantially coextensive with and sheathing the inner tube, and having a separate heat-sealed waterproof seam at its lower end, the seam having a midpoint and laterally extending ends folded about the midpoint and joined together to form an exteriorly accessible pocket into which weighting material may be placed, the inner tube extending into close proximity with the seam of the sheath and conforming to the configuration of the pocket.

2. The blast hole liner of claim 1 including an outer flexible tubular shell enclosing and contoured to the bottom end of the sheath.

3. The blast hole liner of claim 1 wherein the lower edge of the liner projects outwardly from the seam to define a graspable tab useful for opening the pocket for insertion of weighting material.

4. The blast hole liner of claim 1 wherein the pocket is flattened with the folded and joined seam lying flatly against the inner surface of the pocket to provide the pocket with a V-shaped configuration.

5. The blast hole liner of claim 4 wherein the inner tube and outer sheath are of themoplastic, heatsealable material, and wherein the waterproof seal of the inner liner and the waterproof seam of the sheath are separate heat seals to provide the liner with separate waterproof enclosures.

6. The blast hole liner of claim 5 wherein the inner tube is polyethylene having a thickness of from about 0003-0012 inches and wherein the outer sheath is polybutylene having a thickness of approximately half that of the polyethylene.

7. A reinforced, waterproof, flat-storable, blast hole liner with integral weight pocket comprising:

a flattened, flexible, plastic, tubular inner tube terminating at its lower end in a waterproof heat seal and having a lengthto-diameter ratio of at least 20/ l;

a flattened, flexible, plastic, tubular outer sheath substantially coextensive with and sheathing the inner tube and having a separate, heat-sealed, waterproof seam transversely of its lower end, the seam having a midpoint and laterally extending ends defining two seam halves, one seam half being folded upon and heat sealed along its length to the other seam half to form an exteriorly accessible pocket into which weighting material may be placed, the lower end of the sheath projecting outwardly from the seam to form an elongated, graspable tab, and the heat-sealed end of the inner tube extending into close proximity with the bottom end of the sheath,

whereby the tab may be pulled outwardly to open the pocket for insertion of weighting material, the latter retaining the lower end of the inner tube within the lower end of the sheath, and whereby upon insertion of the weighted blast hole liner into a blast hole, the inner tube is anchored to the bottom of the hole by the weighting material.

8. The blast hole liner of claim 7 wherein the pocket is flattened with the seam lying against the inner pocket surface to provide the pocket with a V-shaped configuration with the midpoint of the seam at the apex of the V.

9. The blast hole liner of claim 7 wherein the inner tube is of low density polyethylene blown film having a thickness of about 0.007 inches and wherein the outer sheath is of isotactic poly(butene-l) blown film having a thickness of about 0.004 inches.

10. The blast hole liner of claim 8 including a separate, outer shell of heat-sealable plastic film conformed to the pocket and having a length-to-diameter ratio of not more than 3/l.

11. Method of making a flat-storable, reinforced, waterproof blast hole liner with an integral weight pocket which comprises:

providing a flattened, flexible, waterproof inner tube having a waterproof seal at its lower end with a flexible, waterproof, flattened, tubular outer sheath having a separate transverse waterproof seam at its lower end, the lower end of the inner tube extending into close proximity with, but spaced from the transverse waterproof seam at the lower end of the outer sheath, the latter transverse seam having ends extending generally laterally from its midpoint to define two seam halves,

folding the transverse seam about its midpoint and joining the transverse seam halves together to form a pocket, and flattening the pocket into a V-shaped configuration with the seam lying against the inner surface of the pocket, the seam midpoint fonning the apex of the V,

12. The method of claim 11 wherein the bottom end of the sheath extends beyond the transverse seam and joint between the seam halves to define an outwardly projecting, graspable tab for opening the pocket.

13. The method of claim 1 1 including providing over the infolded, outer sheath an outer, flexible shell extending substantially to the lower end of the sheath, and including the shell in the joint joining the seam halves together, whereby the shell conforms to and becomes a part of the pocket.

14. The method of claim 12 wherein the shell has a length-to-diameter ratio of not more than 3/1.

15. The method of claim 11 wherein the tube and sheath are of heat-scalable, thermoplastic film and wherein the seal at the bottom of the tube, the seam at the bottom of the sleeve, and the joint joining seam halves together are heat seals.

16. The method of claim 15 wherein the inner tube is of low density polyethylene, the outer sheath is of isotactic poly(butene-1), and the heat seal at the bottom of the tube is separate from the heat-sealed seam at the bottom of the sheath.

17. A reinforced, waterproof blast hole liner with an integral weight pocket comprising:

a flexible, waterproof tubular inner tube terminating at its lower end in a waterproof seal and having a length to diameter ratio of at least 20/1;

a flexible, waterproof tubular outer sheath substantially coextensive with and sheathing the inner tube and having a separate, transverse waterproof seam at its lower end, the seam having a midpoint and laterally extending ends folded about the midpoint and joined together to form an exteriorly accessable pocket, the inner tube extending into close proximity with the seam of the sheath and conforming to the configuration of the pocket, and

weighting material carried within the pocket to cause the latter to assume a generally conical configuration for easy insertion into a blast hole, the weighting material pinching shut the lower end of the inner tube, and anchoring the inner tube within the outer sheath when the blast hole liner has been lowered to the bottom of a blast hole.

18. The blast hole liner of claim 17 wherein the inner tube is of low density polyethylene and the outer sheath is of polybutulene of a thickness approximately half that of the inner tube. 

1. A reinforced, waterproof, flat-storable blast hole liner with integral weight pocket comprising: a flattened, flexible, waterproof, tubular inner tube terminating at its lower end in a waterproof seal and having a length-to-diameter ratio of at least 20/1; a flattened, flexible, waterproof, tubular outer sheath substantially coextensive with and sheathing the inner tube, and having a separate heat-sealed waterproof seam at its lower end, the seam having a midpoint and laterally extending ends folded about the midpoint and joined together to form an exteriorly accessible pocket into which weighting material may be placed, the inner tube extending into close proximity with the seam of the sheath and conforming to the configuration of the pocket.
 2. The blast hole liner of claim 1 including an outer flexible tubular shell enclosing and contoured to the bottom end of the sheath.
 3. The blast hole liner of claim 1 wherein the lower edge of the liner projects outwardly from the seam to define a graspable tab useful for opening the pocket for insertion of weighting material.
 4. The blast hole liner of claim 1 wherein the pocket is flattened with the folded and joined seam lying flatly against the inner surface of the pocket to provide the pocket with a V-shaped configuration.
 5. The blast hole liner of claim 4 wherein the inner tube and outer sheath are of themoplastic, heat-sealable material, and wherein the waterproof seal of the inner liner and the waterproof seam of the sheath are separate heat seals to provide the liner with separate waterproof enclosures.
 6. The blast hole liner of claim 5 wherein the inner tube is polyethylene having a thickness of from about 0.003-0.012 inches and wherein the outer sheath is polybutylene having a thickness of approximately half that of the polyethylene.
 7. A reinforced, waterproof, flat-storable, blast hole liner with integral weight pocket comprising: a flattened, flexible, plastic, tubular inner tube terminating at its lower end in a waterproof heat seal and having a length-to-diameter ratio of at least 20/1; a flattened, flexible, plastic, tubular outer sheath substantially coextensive with and sheathing the inner tube and having a separate, heat-sealed, waterproof seam transversely of its lower end, the seam having a midpoint and laterally extending ends defining two seam halves, one seam half being folded upon and heat sealed along its length to the other seam half to form an exteriorly accessible pocket into which weighting material may be placed, the lower end of the sheath projecting outwardly from the seam to form an elongated, graspable tab, and the heat-sealed end of the inner tube extending into close proximity with the bottom end of the sheath, whereby the tab may be pulled outwardly to open the pocket for insertion of weighting material, the latter retaining the lower end of the inner tube within the lower end of the sheath, and whereby upon insertion of the weighted blast hole liner into a blast hole, the inner tube is anchored to the bottom of the hole by the weighting material.
 8. The blast hole liner of claim 7 wherein the pocket is flattened with the seam lying against the inner pocket surface to provide the pocket with a V-shaped configuration with the midpoint of the seam at the apex of the V.
 9. The blast hole liner of claim 7 wherein the inner tube is of low density polyethylene blown film having a thickness of about 0.007 inches and wherein the outer sheath is of isotactic poly(butene-1) blown film having a thickness of about 0.004 inches.
 10. The blast hole liner of claim 8 including a separate, outer shell of heat-sealable plastic film conformed to the pocket and having a length-to-diameter ratio of not more than 3/1.
 11. Method of making a flat-storable, reinforced, waterproof blast hole liner with an integral weight pocket which comprises: providing a flattened, flexible, waterproof inner tube having a waterproof seal at its lower end with a flexible, waterproof, flattened, tubular outer sheath having a separate transverse waterproof seam at its lower end, the lower end of the inner tube extending into close proximity with, but spaced from the transverse waterproof seam at the lower end of the outer sheath, the latter transverse seam having ends extending generally laterally from its midpoint to define two seam halves, folding the transverse seam about its midpoint and joining the transverse seam halves together to form a pocket, and flattening the pocket into a V-shaped configuration with the seam lying against the inner surface of the pocket, the seam midpoint forming the apex of the V.
 12. The method of claim 11 wherein the bottom end of the sheath extends beyond the transverse seam and joint between the seam halves to define an outwardly projecting, graspable tab for opening the pocket.
 13. The method of claim 11 including providing over the infolded, outer sheath an outer, flexible shell extending substantially to the lower end of the sheath, and including the shell in the joint joining the seam halves together, whereby the shell conforms to and becomes a part of the pocket.
 14. The method of claim 12 wherein the shell has a length-to-diameter ratio of not more than 3/1.
 15. The method of claim 11 wherein the tube and sheath are of heat-sealable, thermoplastic film and wherein the seal at the bottom of the tube, the seam at the bottom of the sleeve, and the joint joining seam halves together are heat seals.
 16. The method of claim 15 wherein the inner tube is of low density polyethylene, the outer Sheath is of isotactic poly(butene-1), and the heat seal at the bottom of the tube is separate from the heat-sealed seam at the bottom of the sheath.
 17. A reinforced, waterproof blast hole liner with an integral weight pocket comprising: a flexible, waterproof tubular inner tube terminating at its lower end in a waterproof seal and having a length to diameter ratio of at least 20/1; a flexible, waterproof tubular outer sheath substantially coextensive with and sheathing the inner tube and having a separate, transverse waterproof seam at its lower end, the seam having a midpoint and laterally extending ends folded about the midpoint and joined together to form an exteriorly accessable pocket, the inner tube extending into close proximity with the seam of the sheath and conforming to the configuration of the pocket, and weighting material carried within the pocket to cause the latter to assume a generally conical configuration for easy insertion into a blast hole, the weighting material pinching shut the lower end of the inner tube, and anchoring the inner tube within the outer sheath when the blast hole liner has been lowered to the bottom of a blast hole.
 18. The blast hole liner of claim 17 wherein the inner tube is of low density polyethylene and the outer sheath is of polybutulene of a thickness approximately half that of the inner tube. 